Manual:Infantry Manual:Organization:Cryptography

Cryptography
Cryptography comes from the ancient Greek word kryptós, meaning "hidden, secret". It is the means for secur-ing communication in the presence of an adversary. The goal of cryptography is simple: to prevent someone from reading private messages. Prior to the modern age, there wasn’t much difference between cryptography and encryption, it was the same basic operation. Typically, it was simple letter substitution. These came in many forms – reverse alphabet, half-reversed alphabet, numbers for letters, and reversed words are just a few examples. World War I saw the invention of rotor cipher machines, which allowed the code to be more random and complex. With the invention of computers in World War II, cryptography came of age.

Types of Encryptions
Caesar Cipher The Caesar Cipher dates to the days of the Roman Empire. It’s named after the Roman Emperor Julius Caesar who used it to encrypt his military correspondence. Simply put, a Caesar Cipher is a substitution cipher. The sender chooses letters to represent other let-ters. It can be completely random or something as simple as a letter shift where Z repre-sents A in the cipher. If the receiver has the same decoding key as the sender, they can decipher the encrypted message. Scytale A scytale was a form of encryption used by the Spartan military. A scytale is a trans-position cipher where a piece of leather is wrapped around a wooden rod. The mes-sage is then written in a straight line and carried to the next line when the sender reaches the end of the leather strip. The strip is then unwound from the wood rod and sent to the receiver.

If the message was intercepted, it was unreadable because the enemy most likely would not have a wooden rod of the correct length & width.

Enigma Machine One of the most famous machines ever used for the purposes of encrypting messages was the German Naval Enigma, which saw widespread use during both the First and Second World War. This machine is beautiful in its simplicity. Basically, it is a wooden typewriter with a series of trigger wheels inside which give you an output on a lighted board. This is then added to by a current board which additionally encrypts the message. Any message encoded with proper Enigma will require the user to not only know the initial settings for the three (four wheeled versions appeared later in World War II, but the fourth wheel was stationary) letter wheels, but also the connec-tions on the plug board. All of this was done to confound the enemy to the message that was being delivered, and for the longest time, it worked.

What eventually killed the Enigma’s effectiveness was the hard work of the men and women of Bletchly Park in England. Through the sacrifice of the Poles, who got them their first working copy of the encoding wheels & plug board, to their use of the Tu-ring Bombe, a giant computer of sorts, the Enigma Messages of the German Naval Forces were soon being read in almost real time. This was no small undertaking, considering the limited Computer ability in the 1940’s. From World War II onward, encryption, & Naval Encryption has become more advanced.

Modern cryptography
Modern Cryptography is a combination of mathematics, physics, computer science, communication science, and electrical engineering. And while cryptography is used in everyday applications like passwords, e-commerce, currency (such as BitCoin), and public/civilian electronic communication protection, where it is most critical is in military communications.

In general, there are three types of cryptography: Symmetric Key Cryptography, Asymmetric Key Cryptog-raphy, and Hash Functions. While the methods for each type differ, they all have the same basic process. Plaintext is converted to a coded or ciphertext, which is making the text garbled enough such that the intend-ed receiver of the text can only decode it if they have the key. This process is known as encryption. The pro-cess of converting the gibberish back to plaintext is known as decryption.

Symmetric Key Cryptography Symmetric encryption is one of the oldest and most widely used encryption techniques. Symmetric Key Cryptography uses a single common key. Both the sender and the receiver must have the same key for this type of coding to work. Symmetric Key Cryptography is widely used in today’s Internet and primarily consists of two types of algorithms, Block and Stream. A block cipher breaks down plaintext mes-sages into fixed-size blocks before converting them into ciphertext using a key, en-crypting the information bit-by-bit. A stream cipher, conversely, breaks a plaintext message down into single bits, which then are converted individually into ciphertext using key bits. While symmetric key systems tend to be faster and simpler, the prob-lem is that sender and receiver must somehow exchange key in such a way that no one else has it.

Asymmetric Key Cryptography. Asymmetric cryptography is also called public-key cryptography. It’s a process that uses a pair of related keys – a private key and a public key -- to encrypt and decrypt a message and protect it from unauthorized access or use. The primary benefit of asymmetric cryptography is increased data security is the primary benefit of asym-metric cryptography. Because users are never required to reveal or share their pri-vate keys, it is the most secure encryption process as it decreases the chances of a cybercriminal discovering a user's private key during transmission. Many protocols rely on asymmetric cryptography, including the protocols which make HTTPS possi-ble: transport layer security (TLS) and secure sockets layer (SSL).

Hash Functions A Hash Function is a function that doesn’t use a key. It converts an alphanumeric or alphanumeric key to a small integer value. That mapped integer value is used as an index in the hash table. To simplify it, the hash function maps a significant number or string to a small integer that can be used as the index in the hash table. There are several different hash functions that use numeric or alphanumeric keys. Four examples are Divi-sion Method, Mid Square Method, Folding Method, and Multiplication Method. Many operating systems use hash functions to encrypt passwords.

Advantages of Cryptography
There are many advantageous features of cryptography. These include confidentiality (only the intended re-cipient gets the message), integrity (the data can’t be modified while in transition without it being detected), and authentication (the identities of the parties sending and receiving the data are confirmed through the en-cryption/decryption process